According to clinical observations, virologists appear to have an increased risk of dying of cancer. The present study proposes to test this observation by a case-control study of deaths in physician virologists. Physicians will be identified among lists of deceased members of societies to which virologists frequently belong. Cancer deaths and controls will then be selected from this group. Virolgoists will be identified by means of publications. The causes of death of physicians who have worked with oncogenic viruses will be compared to those of physicians engaged in clinical activities to see if the cancer mortality is increased in the former group. Not only could this study indicate whether there is an increased risk of cancer from occupational exposure to viruses but it could also suggest which particular groups of viruses may produce human disease.